The present invention relates to electrical generators. In particular, the invention relates to fluid-cooled electrical generators.
Electrical generators include a rotor core rotationally driving by a shaft connected through a gear box to a prime mover, such as a gas turbine engine. The rotor includes field coils and/or permanent magnets and rotates within a non-rotating outer shell, or stator core. The stator core includes coiled windings such that rotation of the rotor with energized field coils and/or permanent magnets induces an electric current in the stator windings, thus generating electricity. Inefficiencies in the process of converting mechanical power to electrical power produce significant waste heat which must be removed for the generator for the generator to operate continuously. Typically, a cooling fluid, for example air or oil, flows through channels in a stator housing surrounding the stator to absorb the waste heat and carry it from the generator. The cooling fluid, having absorbed the waste heat, flows in a circuit to a heat exchanger and back to the generator. In the heat exchanger, the cooling fluid is cooled by conduction of the waste heat to a second cooling fluid before completing the circuit back to the generator. While a portion of the waste heat may be beneficially employed by the second cooling fluid if heating the second fluid improves its utility, the bulk of the waste heat is eventually absorbed by the ambient environment and is wasted.